Method and apparatus relating to vapor generation



y 1965 F. J. HANZALEK 3,194,020

METHOD AND APPARATUS RELATING TO VAPOR GENERATION Filed March 25, 1963 I 86 GAS nass WALL OUTER WALL "Jl/ FIL //2 40 CENTER WALL l /4 no v DEM.

H R- -4- HTR- 56 54 52 5O 48 INVENTOR FREDERICK J. HANZALEK United States Patent 3,194,020 METHOD AND APEARATUS RELATING TO VAPOR GENERATION Frederick J. Hanzalek, Sufiield, Conn, assignor to Combustion Engineering, Inc., Windsor, Coma, a corporation of Delaware Filed Mar. 25, 1963, Ser. No. 267,511 9 Claims. (Cl. 60-67) This invention relates generally to the art of vapor generation and has particular relation to an improved method and apparatus for high capacity generation of vapor such as employed in the utility field with the invention being particularly concerned with such vapor generators that have a so-called once-through flow circuit through which the once-through flow of the generator is forced by means of the feedwater pump.

In initiating operation of such vapor generators, or in other words in the so-called startup phase of the unit, it is necessary that a minimum flow velocity prevail in the high heat absorption portions (primarily the tube portions associated with the furnace) of the vapor generator in order to insure against overheating and damaging these portions. It is further necessary that the design of the unit be such that tolerable pressure drops throughout the various portions of the once-through flow circuit are produced at the maximum continuous operating load of the unit. In conventional once-through flow vapor generators the design is usually such that approximately 30 percent of maximum fiow through the aforementioned high heat absorption portions of the through-flow circuit is required during startup. The main feedwater pumps, which are high speed, high capacity pumps that develop a very high pressure head, are often driven by steam turbines for reasons of plant economy and efficiency in the over-all plant cycle and because of this high throughflow required at startup, special electric motor driven startup pumps connected in parallel with the main turbine driven feedwater pumps are employed during the startup operation. Auxiliary steam from a separate steam generator is often available for use with these units and is used for a variety of purposes such as turbine seals, de-aeration of feedwater during startup, soot blowing, air preheating and the like. It is, however, uneconomical to provide the very large quantity of auxiliary steam necessary to drive the main feedwater pump at startup with this large 30 percent flow requirement.

In accordance with the present invention there is provided a modified once through-flow vapor generator that has a steam turbine driven main feedwater pump complex with this main feedwater pump being employed during startup as well as during normal operation of the unit. Auxiliary steam is employed to drive the main feedwater pump during startup with the combination as thus employed, eliminating the necessity for the electric motor driven startup pumps heretofore utilized.

The modified once through-flow vapor generator, as this term is employed in the art, is a once-through flow vapor generator which has a recirculation system superimposed upon its through-flow circuit or upon a portion of its through-flow circuit, which portion includes the region of the circuit of highest heat absorption (that portion associated with the furnace) and with this recirculation being effective to increase the flow of fluid through this portion of the through-flow circuit during startup and at least at loads below a predetermined load. The modified once through-flow unit thus requires substantially less through-fiow during the startup operation than the conventional through-flow unit which is not equipped with the superimposed recirculation system. Due to this decrease in through-flow requirement, which may be from the conventional 30 percent requirement to a 10 percent or lower requirement, it is economical to use the steam driven main feedwater pumps during startup and supply the steam to the turbine drives from an auxiliary boiler. In such an arrangement the steam capacity of the auxiliary boiler will not have to be much, if any, greater than its capacity to furnish the normal auxiliary steam requirements of the plant since many of these auxiliary steam requirements are not concurrent with startup requirements of the vapor generator, such as soot blowing, plant heating and the like. Thus, with the invention an economical arrangement for startup is employed utilizing the main steam driven feedwater pumps and with auxiliary motor driven startup pumps being completely eliminated together with the piping, valving and controls necessary with these pumps.

Accordingly, it is an object of the present invention to provide an improved method and apparatus for high capacity vapor generation.

It is a further object of the invention to provide such an improved method and apparatus employing a vapor generator equipped with a through-flow circuit and wherein the main steam turbine driven feedwater pump is employed during startup.

A still further object of the invention is to provide an improved method and apparatus utilizing such a vapor generator and having improved economy and efiiciency during startup operation.

Other and further objects of the invention will become apparent to those skilled in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired as hereinafter more particularly set forth in the following detailed description of an illustrative embodiment, said embodiment being shown by the accompanying drawing wherein the single figure is a diagrammatic representation in the nature of a flow diagram of an improved power plant embodying the present invention.

Referring now to the drawing, wherein like reference characters are used throughout to designate like elements, the illustrative and preferred embodiment of the invention as depicted therein includes a modified once through-flow supercritical vapor generator that supplies vapor to a turbine arrangement which in conventional practice drives an electric generator. The through-flow circuit of the vapor generator includes a number of heat exchange sections which are connected in series fiow relation with these sections being comprised of tubular members. In the illustrative flow diagram the through-flow passes through the feedwater valve 10 and enters the economizer 12. From the economizer the through-flow is conveyed through the furnace center wall 14 then through the outer furnace walls 15 and thereafter through the gas pass walls 18. It will be appreciated that these walls are lined with tubes and that the through-flow is conveyed through the tubular elements lining these walls, and it will be further appreciated that the reference to these heat exchange portions lining the walls is concerned with a conventional high capacity vapor generator organization wherein a fluid cooled gas pass extends from the furnace. For a detailed explanation with regard to the disposition of the tubular members on the walls previously mentioned and the interconnection of these heat exchange sections, reference is made to US. Patent 3,172,396 of Robert A. Kane for Wall Arrangement for Vapor Generator.

After traversing the gas pass wall heat exchange portion of the through-flow system, the through-flow is then conveyed through the series of fluid heaters 20 which may take the conventional form of tubular members disposed in panels in sinuously and internested relation and in the '7 combustion gas stream generated by the burning of fuel generator and with the burner being diagrammatically represented as 24. The vapor whichleaves the finalfiuid heater 20 is;conveyed through. conduit 26 to the high pressure turbine 28 traversing the turbine valves. From the high pressure turbine 28 the steam is conveyed through conduit 32 to the low pressure turbine or low pressure turbine stage 34 and from there through conduits 36 to the condenser 38; While the unit'is disclosed as'operating on the non-reheat cycle, it Will be understood that the .single or double reheat cycle may be employed if desired. 1

conduit 4%) and condensate pump 42 to the demineralizer 44. 7 Then from this demineralizer the water is conveyed through the low pressure heaters 46 to the de-aerator 48.

Feedwater is conveyed from the de-aerator by and through the motor driven feedwater booster pump 50, the inter mediate pressure feedwater heaters 52', then throughthe main feed pump 54 and the high pressure feedwater heaters 56 for passage through the feedwater flow control valve and the through-flow circuit'of the vapor generator. The electric motor driven booster pump 50 is conventionally employed in once-through flow vapor generators to alleviate the problem of the main teed pump pump sufficiently elevates the pressure .at 'the'inlet of the main feed pump so that this problem is alleviated, and the main pump operates in a satisfactory manner. The booster pump is a relatively low-head pump.

As previously mentioned, the modified once'throughflow vapor generator has superimposed on its throughwith regar-dto net positive'suction head. This booster I flow. circuit, including the portion of the circuit which g has the highest rate of heatabsorption, a recirculating system with this recirculating system including the recirculating conduit '58 the inlet of which is connected to the through-flow circuit at'the outlet of the gas pass walls heat exchange section 18 and the outlet of which is connected with the mixing vessel fill wherein the hot recirculating fluid is mixed with the cooler fluid that is received in this vessel from the outlet of the economizen.

In the illustrative embodiment the recirculating pump 62 is in series flow with the through-flow circuit being connected at the outlet of the mixing vessel 60*. This recirculating pump 62 does not have to operate against any substantial head but merely overcomes the friction head developed in thecircuit through which it forces the fluid. Suitable valves 64 are provided upstream and downstream of this recirculating pump and a bypass 66 is provided around the, pump and valves and in which is disposed check valve 68. For a detailed explanation of the theory of the recirculation system that forms a part of the modified once through-flow steam generator refer-. ence is made to US. Patent 3,135,252 of Willburt W.

Schroedter dated June 2, 1964. V

Connected in the through-flow circuit intermediate the gas pass wall heat exchange'portion thereof and the first of the fluid heaters. 20, is a boiler throttle valve 74 and in bypass relation with this boiler throttle valve, is the boiler throttle bypass valve'72gThere is provided a system in bypass'relation with both of thcsevalves which is used to provide vapor flow through the fluid heaterslfl and to the turbine 28 during the initiation portion of the startup of the unit with this system including the conduit 1 I 4 76is connected with the hot well of the condenser by means of conduit 84- in which conduit is provided the valve 86.

In the'startup of the unit the through-flow circuit is filled up to the BT and BTB valves 70 and 72 by means of the electric motor driven feedwater booster pump 50.

Thereafter the recirculating pump 62 isactivated so that a recirculation of fluid through the furnace wall tubes and the gas pass walljtubes is provided. The main feedwater pump, 54 is activated to provide a through-flow through the portion :of the through-flow circuit upstream 'of theboiler throttle valve' 70 and the boiler throttle 7 V the flash tank 76. The valve 78 is set to provide a pre- From condenser 38 the condensate is conveyed through determinedrelatively high pressure in the through-flow system. The burner or burners 24 are lit off and the initial heating of the fluid commenced. 7

' Theboiler water feed pump 54 is driven by means of the turbine 88 and during the startup procedure, until sufficient steam for driving the turbine is generated by the, vapor generaton'this turbine 88 is provided with steam from auxiliary boiler 90. Such an auxiliary boiler is customarilyrprovided with these large high capacity 'units with this boiler generatingauxiliary steam for a large variety. of. purposes such as turbine sealing, de-

aerating during cleanup, soot blowing, air preheating,

operation of vacuum jets for condensers, plant heating and others. This auxiliary boiler as illustratively disclosed is fired by burner 92 and it produces steam at some desired pressure. As disclosed this boiler supplies steam for the turbine seals of the main turbine through conduit 94- and supplies steam through conduit 96 to the turbine 88 with valve 98 controlling the flow of this auxiliary steam to the turbine. Auxiliary steam is also supplied through conduit 1% to the tie-aerator with valve 102 controlling 'thisflow of auxiliary steam.

Since the auxiliary boiler is required to be of a capacity a to supply the many needs for which it is used in the system and since some of these needs are not concurrent with and;do not prevail at the time of starting up the costs in that separate electric motordriven startup pumps unit, this boiler has a capacity which may be used to supply a limited amount of steam to the turbine 88 that 'drives the main feedwater pump. Since with the -modified once through-flow unit the amount of through-flow necessary: at startup is relatively low, the auxiliary steam requirement to drive the turbine 88 duringstartup is such that the utilization of the main feedwater pump during the startup operation has been found to be economically feasible and resulting in a saving in operating and capital are not required.

As the fluid is heated up during the initial portion of the startup procedure, a portion of this fluid flashes to steam as it passes through the valve 78 and into the flash tank 76. a This steam is conveyed through theconduit 80 and thehce throughthe fluid heater 20. When the quantity and pressure of this steam is suflicient, it may be admitted to the turbine for, heating, rolling and synchronizing the same. 5 The water in theflash tank is conveyed to the condenser hot well through the conduit 84. As the temperature is increased in the through-flow circuit upstream of theBT valve and the BTB valve 72 and the vapor delivered to the turbine increases and the BT valve 70 isbpened. g

. The turbine v88 is supplied with auxiliarysteam from the auxiliary boiler 'flluntil suflicient steam has been produced'by the vapor generator for driving this turbine. For this purpose the temperature and pressure of. the steam leaving the vapor generator and zbeing conveyed through conduit 26 must at least be equal to the temperature and pressure of the vapor produced by the auxiliary boiler. When the vapor generator has produced steam of a sufficient temperature and pressure for operating the turbine 88, the operation of this turbine will be transferred from the auxiliary boiler and it will be supplied with vapor generated in the vapor generator. For this purpose conduit 104 is connected with conduit 26 with the flow through the conduit 104 being controlled by valve 106. For greatest cycle efficiency at and above a predetermined main generator load such as /3 of maximum load, the turbine 88 is driven by so-called extraction steam, i.e. steam taken from a predetermined extraction point of the high pressure turbine. As disclosed, this extraction steam is conveyed through conduit 108 with valve 110 controlling the supply of this steam to turbine 88. Extraction steam from a suitable extraction point is also conveyed through conduit 112 to the deaerator with valve 114 controlling the supply of this steam to the de-aerator. During normal operation of the vapor generator at loads below approximately /3 of the maximum load, the extraction steam may be supplemented by steam taken from the main steam supply to the turbine or in other words below approximately /3 load steam may be supplied to the drive turbine 88 for the main feedwater pump through extraction conduit 108 and the conduit 1G4 both in parallel.

While the turbine 88 may be of the condensing type for the purposes of the present invention it is shown of the non-condensing type with the steam exhausted from the turbine being conveyed to the de-aerator.

It will be appreciated that the illustrative feedwater supply system depicted in the drawing is diagrammatic in nature and that in an actual installation there may be more than one so-called string of feedwater heaters, and the main feedwater pump complex may consist of two pumps connected in parallel each with their own turbine drives and with the combined capacity of these pumps being such as to provide the necessary feedwater flow for full load operation.

Accordingly, there is provided with the present invention a novel combination utilizing the main steam driven feedwater pump during the startup of a combined circulation vapor generator.

While I have illustrated and described a preferred embodiment of my invention it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without depart ing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

What I claim is:

1. A once-through flow vapor generator having a through-flow circuit that includes a plurality of heat exchange sections connected in series flow relation with a recirculating system superimposed on the through-flow system including the region thereof that has the highest rate of heat absorption, said recirculating system being operative during start up of the generator, said generator having a main feed pump, a turbine operative to drive said pump, and an auxiliary vapor generator operatively connected to supply vapor to said turbine during said startup of the said one-through flow vapor generator.

2. In a forced once-through flow tubular vapor generator having a through-flow circuit, a circulating system superimposed on a predetermined portion of said circuit including the portion having the highest rate of heat absorption during startup and which system is operative to provide a circulation of the working medium through said circuit portion at least at and below a predetermined load, and a vapor turbine driven feed pump, the improved method utilized during startup of providing a predetermined through-flow via the main feed pump, supplying the motive fluid to the pump drive from a source separate from said vapor generator, said predetermined throughfiow being below minimum flow requirements for protection of said circuit portion of highest rate of heat absorption, supplementing the through-flow through said circuit portion by recirculation so that it is at least said minimum, raising the temperature and pressure of the throughflow and when vapor of at least the temperature and pressure of said separate source is produced transferring from said separate source for driving the turbine of the feed pump to the vapor produced in the vapor generator.

3. In the initiation of operation of a modified oncethrough flow tubular vapor generator wherein the flow through the portion of the generator of highest heat absorption is a combination of through-flow and recirculation flow with the through-flow per 'se being considerably under that necessary to provide the minimum required flow for tube protection through said portion the improvement characterized by producing said through-flow at said initiation of operation by means of the main feedwater pump, driving said pump by a vapor turbine and supplying the vapor motive medium to said turbine from an auxiliary boiler.

4. The method of generating steam comprising establishin g a flow of the working medium through a continuous path by means of a steam turbine driven main feedwater pump, imparting heat to said working fluid as it traverses said path converting the same to a vapor, establishing a recirculation of said working medium about a predetermined portion of said path including the portion of highest heat absorption, initiating the flow through said path by supplying steam from an auxiliary source to the turbine drive for said main feedwater pump with this initial flow being insufficient for tube protection at said region of highest heat absorption but with the recirculation making up for the insufiiciency of the through-flow for this purpose and transferring the delivery of steam to said turbine from said auxiliary source to steam produced in said continuous path when the pressure and temperature of this latter steam is such that it at least equals that of the auxiliary source.

5. In a once-through flow vapor generator having a through-flow circuit that includes a plurality of heat exchange sections connected in series flow relation with a recirculating system superimposed on the through-flow system including the region thereof that has the highest rate of heat absorption, said generator having a vapor driven turbine main feed pump the turbine of which receives as its operating medium during normal operation of the vapor generator vapor that is produced in said generator, said unit having the characteristic that the startup through-flow requirements are substantially less than the flow requirements necessary forprotection of the portion of the through-flow circuit of highest heat absorption with the recirculating system assuring adequate protection of this portion of the circuit the method characterized by establishing the through-flow that is provided at startup of the unit by the vapor driven main feed pump and supplying the vapor for the turbine drive of said pump during startup from an auxiliary source.

6. A vapor generator of the once through-flow type that includes a plurality of heat exchange sections in series flow relation one of which sections comprises tubular members lining the walls of the furnace, a circulating system superimposed on a portion of the throughflow circuit including said furnace wall tubes, a valve in said circuit downstream of said portion but upstream of a number of the final heat exchange sections, a flash tank, valved conduit means connecting said flash tank to the through-flow circuit upstream of said valve, valved conduit means connecting the upper portion of the flash tank to said through-flow circuit downstream of said valve, a water discharge connected with the lower region of said tank, a vapor turbine driven main feedwater pump for forcing the through-flow through said circuit, an auxiliary boiler operatively connected with the turbine for driving said pump during startup of the vapor generator and means for supplying to said turbine vapor produced in the vapor generator.

' pump, an auxiliary boiler operatively connected with said 7. In a once-through fiow vapor generator having a A through flow circuit including a plurality of heat excirculation of fluid through a portion of the throughflow circuit including the region of highest heat absorption, establishing a through-flow by means of the main feedwater pump and of such a magnitude that perv se it doesnot provide'the necessary velocity for :protection of the furnace tubes but together with the recirculation sutficient'velocity 'for this purpose is had, driving said feedwater pump by means of a vapor turbine and supplying the motive fluid for said vapor turbine during startup of the vapor generator from an auxiliaryboiler and transferring the supply of such boiler fluid to vapor generated by the vapor generator-after the startup op eration has progressed sufficiently so that. the generator is producing adequate vapor for this purpose.

8. A once-through fiow'v'apor generator comprising in combinationathrough-flow circuit including a p111: rality of heat exchange sections connected in series flow relation, a turbine driven mainfcedwater pump operative to force. the through-flow through said circuit one of said heat exchange sections of said circuit including furnace wall tubes, a recirculation system superimposed ona portion of said circuit including said furnace wall tubes and operative to provide for a recirculation of fluid through said portion, a main turbine connected to receive steam from said vapor, generator, an auxiliary boiler operatively connected to supply-vapor to the turbine drive for the main feed'pump during startup, means connected with an intermediate pointof said main turbine for supplying vapor to said turbine drive and means connected intermediate the vapor generator and the main turbine for supplying vapor to said turbinedrive and valve means operative to; control the supply of steam.

from these last two locations and from the auxiliary boiler to the turbine drive for the, main feed pump.

9. A once-through flow steam generator including a and at startup in order to protect these portions-fromoverheating, a main feed pump, a turbine drive for said termined' load is reached. r

turbinedrive to supply steam thereto during startup, and means for transferring'thesupply' of steam from said auxiliary boiler to" the steam generator after a prede- References fitted by the Applicant UNITED STATES PATENTS 1,064,855 6/13 Parry. a 1,791,923 2/31 Eule. 1,892,093 12/ 32 Battistella, 2,556,128- 6/51 Webb. 2,858,808 11/58 Rowand'. 1

2,907,305 10/59 Profos. 2,989,038 6/ 61 Schwarz. 3,009,325 11/61 Pirsh; 3,010,853 11/61 Elliott. 3,019,774 2/62' Beyerlein. 3 ,038,45 3 6/62 Armacojst. 3,085,915, ,4/63 'Heitrnann-et al. 3,159,145 12/ 64 Strohrne yer. J 3,162,179 12/64 Strohrneyer.

1 FOREIGN PATENTS 617,110- 3/61 Canada. 386,042 l/21 Germany. 768,201 I 2/57 Great'Britain.

' OTHER REFERENCES Combustion of April 1962, pages 28-38.

. Article by C. A. Dauber entitled Avon No; A Supercritical Pressure Plant appearing in Combustion of August 1956, pages 47-56. r

V Large'Sub; and Supercritical Steam Generator Startup and Control System Integration With the Turbine Generator by Charles Strohmeyer, In, pages 1-17 and Figs. 5-10 published by Gilbert Associates, Inc., March 1962.

V, ASME article Paper No. -WA-51 by Charles Strohmeyer, In, presented at Winter Annual Meeting ASME,

Nov. ,27-Dec. 2, 1960, pages 1-12.

Mitteilungen No. 1, September 1956, D'orrwerke- 

1. A ONCE-THROUGH FLOW VAPOR GENERATOR HAVING A THROUGH-FLOW CIRCUIT THAT INCLUDES A PLURALITY OF HEAT EXCHANGE SECTIONS CONNECTED IN SERIES FLOW RELATION WITH A RECIRCULATING SYSTEM SUPERIMPOSED ON THE THROUGH-FLOW SYSTEM INCLUDING THE REGION THEREOF THAT HAS THE HIGHEST RATE OF HEAT ABSORPTION, SAID RECIRCULATING SYSTEM BEING OPERATIVE DURING START UP OF THE GENERATOR, SAID GENERATOR HAVING A MAIN FEED PUMP, A TURBINE OPERATIVE TO DRIVE SAID PUMP, AND AN AUXILIARY VAPOR GENERATOR OPERATIVELY 